They didn't see fit to qualify the claim, so let me point out that the songs in question are only mainstream USA/EURO songs and 'all time' means the last 60 years. There were some pretty good songs in the 1920s and they've been singing widely in India for centuries. Still, Rolling Stone's 500 Greatest Songs of All Time is worth a look.

While researching on a project about the psychology of music I ran across this article by Christine Kenneally at the Boston.com
It covers a lot of ground in a few words. This edited bit is especially pithy.

Music is one of the human species's relatively few universal abilities. Without formal training, any individual, from Stone Age tribesman to suburban teenager, has the ability to recognize music and, in some fashion, to make it.

Why this should be so is a mystery... Modern culture, in all its technological extravagance, springs directly from the human talent for manipulating symbols and syntax. Scientists have always been intrigued by the connection between music and language. Yet over the years, words and melody have acquired a vastly different status in the lab and the seminar room.

While language has long been considered essential to unlocking the mechanisms of human intelligence, music is generally treated as an evolutionary frippery -- mere "auditory cheesecake," as the Harvard cognitive scientist Steven Pinker puts it.

But thanks to a decade-long wave of neuroscience research, that tune is changing. A flurry of recent publications suggests that language and music may equally be able to tell us who we are and where we're from -- not just emotionally, but biologically.

To grasp the originality of this idea, it's necessary to realize two things about how music has traditionally been understood. First, musicologists have long emphasized that while each culture stamps a special identity onto its music, music itself has some universal qualities.

For example, in virtually all cultures sound is divided into some or all of the 12 intervals that make up the chromatic scale -- that is, the scale represented by the keys on a piano. For centuries, observers have attributed this preference for certain combinations of tones to the mathematical properties of sound itself.

This music-is-math idea is often accompanied by the notion that music, formally speaking at least, exists apart from the world in which it was created. Writing recently in The New York Review of Books, pianist and critic Charles Rosen discussed the long-standing notion that while painting and sculpture reproduce at least some aspects of the natural world, and writing describes thoughts and feelings we are all familiar with, music is entirely abstracted from the world in which we live.

Music is still a mystery, a tangle of culture and built-in skills that researchers are trying to tease apart. No one really knows why music is found in all cultures, why most known systems of music are based on the octave, why some people have absolute pitch and whether the brain handles music with special neural circuits or with ones developed for other purposes. Recent research, however, has produced a number of theories about the brain and music.

A highly publicized study in the mid-'90s found that he "Mozart effect," led children who regularly listened to Mozart had higher IQs.

But critics pointed out that well-educated parents often listen to classical music, and have the money for music lessons, and, because IQ is partly hereditary, it's genetics that accounts for the child's IQ edge.